Radio communication system

ABSTRACT

In a wireless communication system, a central control unit  31  comprises a synchronizing means for synchronizing a frame for an base station-mobile station communication with that for an inter-mobile station direct communication based on control information used for the base station-mobile station communication, when a second frequency is used for the inter-mobile station direct communication which is different from a first frequency used for the base station-mobile station communication. The central control unit  31  also comprises an allocation means for allocating a band and a frequency for the inter-mobile station direct communication in accordance with an allocation request from a base station  30  or a mobile station  40 . Frames for the base station-mobile station communication and the inter-mobile station direct communication are synchronized by utilizing control information  55  for the base station-mobile station communication instead of the conventional control information provided by the mobile station. The system allows a base station-mobile station communication to take place even when an inter-mobile station direct communication is conducted at a frequency other than that of the base station. As the base station controls the inter-mobile station direct communication, the burden on the mobile stations can be reduced, and a single base station can use multiple frequencies simultaneously.

TECHNICAL FIELD

[0001] The present invention relates to a wireless communication systemcomprised of a base station and mobile stations, particularly to animprovement relating to inter-mobile station direct communication in awireless communication system based on a TDMA (Time Division MultipleAccess) system.

BACKGROUND ART

[0002] A wireless communication system is comprised of a base stationfor giving notices of allocations of bands (time regions forcommunications) and a plurality of mobile stations based on the TDMAsystem (in which different time regions are allocated to the mobilestations at the same frequency for carrying out communication). For sucha system, a PHS inter-mobile station direct communication system inaccordance with RCR STD-28 (second-generation cordless telephone systemstandard, version 1) of ARIB (Association of Radio Industries andBusinesses) has been proposed as a method of carrying out inter-mobilestation direct communication at a frequency other than that used by thebase station. Improvements of the system are disclosed in JP PatentPublication (Kokai) Nos. 11-122663 A1(1999) and 11-341564 A1(1999), forexample.

[0003]FIG. 13 shows an example of the frame structure in the TDMAwireless communication system.

[0004] As shown in FIG. 13(a), a length of time in which the samefrequency is used for communication is divided into frames 1 atpredetermined time intervals. In each frame (at predetermined periods),the base station transmits control information 2 to all of the mobilestations in a wireless LAN area created by the base station. The controlinformation 2 includes information allowing the multiple mobile stationsto be synchronized with the base station, and information indicating theband (time region) within the frame allocated to each mobile station.

[0005] The frame is divided into the time regions of DOWN-LINK3 for thetransmission of data from the base station to the mobile stations andUP-LINK4 for the transmission of data from the mobile stations to thebase station. In each time region, each mobile station is allocated aband 5 (band A) and a band 6 (band B), as shown in FIG. 13(b), such thatthe base station and the mobile stations can communicate with oneanother bi-directionally.

[0006] The control information 2 will be hereafter described byreferring to FIG. 13(c).

[0007] Generally, in the physical layer of wireless systems, a digitalsignal comprised of a preamble 200 for broadcast and a data payload 201(data payload 1, . . . , data payload N), which is information data fortransmission, is converted into an electric signal. The preamble 200located at the head identifies the signal received from a wirelessinterface. Particularly, the preamble 200 for broadcast that is attachedwhen the base station transmits broadcast information into a wirelesscell functions as a synchronization signal with which a mobile stationin the wireless cell attempts to achieve synchronization with the basestation. Further, the control information 2 includes such controlinformation as frame structure information and band allocationinformation.

[0008]FIG. 14 shows a block diagram of an example of the configurationof a wireless LAN based on the above-described wireless communicationsystem.

[0009] In FIG. 14, numeral 7 designates a WAN (Wide Area Network), andnumeral 8 designates a wireless LAN (Local Area Network). The wirelessLAN 8 is comprised of a plurality of mobile stations 11-13 and a basestation 10. The base station 10 is either connected to a central controlunit 9 for the central control of band allocations, or is equipped withthe central control unit 9 inside. The wireless LAN 8 is connected tothe WAN 7 via the base station 10.

[0010] The mobile stations 11 to 13 carry out a base station-mobilestation communication according to the band allocation informationnotified by the base station 10. The communication paths are indicatedas communication paths 14-16. The communication path for directcommunication between a mobile station 11 (mobile station <1>) and amobile station 12 (mobile station <2>) is indicated by a communicationpath 17.

[0011] When the mobile station 11 (mobile station <1>) transmits data tothe mobile station 12 (mobile station <2>), if the normal basestation-mobile station communication is employed, the same data wouldhave to be transmitted twice via the communication paths 14 and 15 shownin FIG. 14, which is inefficient. Thus, it is necessary to use a methodfor carrying out inter-mobile station direct communication by which datais directly transmitted between the mobile stations via thecommunication path 17 without the intervention of the base station 10.

[0012]FIG. 15 shows an example of the frame structure for inter-mobilestation direct communication in a conventional wireless communicationsystem.

[0013] In the example of FIG. 15, inter-mobile station directcommunication is conducted at a frequency different from the one used bythe base station 10. One of the mobile stations that carry outinter-mobile station direct communication transmits control information19 at the frequency for inter-mobile station direct communication. Thisfrequency is different from the frequency at which frame synchronizationis achieved and communications are carried out according to the controlinformation 18 transmitted by the base station. The mobile stations thatcarry out the inter-mobile station direct communication are providedwith a base-station function for synchronizing their frames andallocating bands.

[0014] Other examples of conventional techniques for carrying outinter-mobile station direct communication include: a wireless LAN systemand a PDC (Personal Digital Cellular) portable telephone employing theCSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) systemaccording to the ISO/IEC (International Organization forStandardization/Intemational Electrotechnical Commission) 8802-11 or theIEEE (Institute of Electrical and Electronics Engineers) 802.11standards; HiperLAN according to the ETSI (European TelecommunicationsStandards Institute), which is a 3.5-generation system transitioninginto a 4^(th)-generation system to be standardized around the year 2010following PHS (Personal Handy-phone System) and the W-CDMA (WidebandCode Division Multiple Access); and the MMAC (Multimedia Mobile AccessCommunication System) wireless system according to the ARIB (Associationof Radio Industries and Businesses).

[0015] The IEEE802. 11 and the HiperLAN will be briefly described below,although they do not have direct relevance to the present invention inthat the former is not a centrally controlled wireless system comprisinga central control unit for centrally controlling band allocations, andthat the latter is a system that employs the same frequency as that forbase station-mobile station communication.

[0016]FIG. 16 shows an example of communication according to theIEEE802.11 system.

[0017] In FIG. 16, among mobile stations 1 to 4 in a wireless LAN area20, when a mobile station <1>wishes to send information to a mobilestation <2>, the mobile station <1>broadcasts an RTS (Request to Send)signal 21 and 24. Each mobile station analyzes the RTS signal. When itis not an information transmission request directed to a particularmobile station, the mobile station stands by. When the RTS signal isdirected to a particular mobile station, the mobile station (mobilestation <2>) transmits a CTS (Clear to Send) signal 22 and 25 toindicate that it is ready to receive. In response, the mobile station<1>transmits information via a MAC signal 23 and 26 to the mobilestation <2>. During these processes, the other mobile stations refrainfrom transmission for a certain time period to avoid collision oftransmission signals.

[0018]FIG. 17 shows an example of the frame structure in the HiperLANsystem. Parts or elements similar to those shown in FIG. 13 aredesignated by similar references.

[0019] In the HiperLAN system, a band 28 is provided in a TDMA frame 27for carrying out inter-mobile station direct communication. In this band28, the base station ceases transmission to allow the mobile stations totransmit to each other, thus allowing base station-mobile stationcommunication and inter-mobile station direct communication to takeplace on a single frequency.

[0020] In a conventional wireless communication system, the frames forinter-mobile station direct communication and those for basestation-mobile station communication are not synchronized, as shown inFIG. 15. Thus, in order to obtain control information for synchronizingthe respective frames, the communication modes are switched. This is aprocess in which a mobile station terminates its connection with thebase station for base station-mobile station communication and then setsup a connection with the mobile station that has the base-stationfunction for carrying out inter-mobile station direct communication. Animproved method of obtaining broadcast information from the base stationis proposed by JP Patent Publication (Kokai) No. 11-122663 A1(1999), forexample, in which the switching is carried out intermittently.

[0021] However, the apparatus disclosed in the above publication has theproblem that the mobile station 11 (mobile station <1>) cannot carry outdata communication with the mobile station 12 (mobile station <2>) andthe base station 10 simultaneously, as shown in FIG. 14. In recentcommunication systems, there is an ongoing shift from voicecommunication by telephone to data communication. Thus, the aboveproblem means that, in the context of building a wireless LAN, themobile stations are intermittently cut off from the network, creatingfurther problems. For example, the base station may not be able totransmit data received from a connected WAN (such as the Internet) to adestination mobile station in the wireless LAN, or the base station maynot even recognize the presence of the mobile station due to the absenceof connection therewith.

[0022] The above discussion is based on the assumption of creating, forexample, a household wireless LAN (home network) comprised of a gatewayunit including a base station connected to the Internet outside, andmobile stations including household information appliances (such as arefrigerator, microwave oven, television, video server, or set-top box,for example). In this case, it would be problematic if the externalnetwork could not send video information to the video server when thevideo server is wirelessly transmitting video information to thetelevision, or if, when an air conditioner should be externallyoperated, the presence of the air conditioner on the network could notbe confirmed due to the termination of its connection to the basestation.

[0023] Further, in order to realize inter-mobile station directcommunication, there is the additional problem of having to add thebase-station function to one of the mobile stations that is to act asthe base station.

[0024] It is an object of the invention to provide an efficient wirelesscommunication system that allows for base station-mobile stationcommunication even when inter-mobile station direct communication iscarried out at a frequency other than that of the base station, whichcan reduce the burden on the mobile stations by having the base stationcontrol inter-mobile station direct communication, and which allows aplurality of frequencies to be simultaneously used by a single basestation.

DISCLOSURE OF THE INVENTION

[0025] The invention provides a wireless communication system comprisedof a base station and mobile stations wirelessly connected to the basestation, wherein the mobile stations can communicate with one anotherwithout the intervention of the base station, the system furthercomprising a synchronizing means, wherein

[0026] when a second frequency is used for an inter-mobile stationdirect communication which is different from a first frequency used fora base station-mobile station communication, the synchronizing meanssynchronizes a frame in the base station-mobile station communicationwith that in the inter-mobile station direct communication based oncontrol information used in the base station-mobile stationcommunication.

[0027] The invention provides a mobile station wirelessly connected to abase station and capable of a base station-mobile station communicationat a first frequency and an inter-mobile station direct communication ata second frequency that is different from the first frequency withoutthe intervention of the base station, the mobile station comprising asynchronizing means for synchronizing a frame in a base station-mobilestation communication with that in an inter-mobile station directcommunication based on control information used in the basestation-mobile station communication.

[0028] The invention provides a base station in a wireless communicationsystem comprised of the base station and mobile stations wirelesslyconnected to the base station, the base station comprising an allocationmeans for allocating a second frequency for an inter-mobile stationdirect communication which is different from a first frequency used fora base station-mobile station communication in response to a requestfrom a mobile station.

[0029] The invention provides a base station in a wireless communicationsystem comprised of the base station and mobile stations wirelesslyconnected to the base station, the system capable of conducting a basestation-mobile station communication at a first frequency and aninter-mobile station direct communication at a second frequencydifferent from the first frequency without the intervention of the basestation, the base station comprising:

[0030] an allocation means for allocating bands in a frame for aninter-mobile station direct communication based on a request from amobile station.

[0031] The base station may comprise a carrying means for performingcarrier sensing at a plurality of available frequencies and for carryingavailable frequencies other than a frequency used by the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 shows block diagrams of examples of a base station and amobile station in the wireless communication system according to theinvention.

[0033]FIG. 2 shows an example of the frame structure in an inter-mobilestation direct communication in the wireless communication system.

[0034]FIG. 3 shows a block diagram of an example of a wireless LAN basedon the wireless communication system.

[0035]FIG. 4 shows a control sequence chart illustrating the flow ofdata in an example of communication in the wireless communicationsystem.

[0036]FIG. 5 shows a flowchart of communication processes performed inthe base station in the wireless communication system.

[0037]FIG. 6 shows a flowchart of communication processes performed inthe mobile station in the wireless communication system.

[0038]FIG. 7 shows a control sequence chart illustrating the flow ofdata in the wireless communication system according to the invention.

[0039]FIG. 8 shows a block diagram of band allocations in the wirelesscommunication system.

[0040]FIG. 9 shows a block diagram of frame allocations in the wirelesscommunication system.

[0041]FIG. 10 shows an example of a state of communication between thebase station and the mobile stations in the wireless communicationsystem, and shows a block diagram of frame allocation in the wirelesscommunication system.

[0042]FIG. 12 shows an example of a state of communication between thebase station and the mobile stations in the wireless communicationsystem.

[0043]FIG. 13 shows an example of the frame structure in a conventionalTDMA wireless communication system.

[0044]FIG. 14 shows a block diagram of an example of a wireless LANbased on the conventional wireless communication system.

[0045]FIG. 15 shows an example of the frame structure for aninter-mobile station direct communication in the conventional wirelesscommunication system.

[0046]FIG. 16 shows an example of communication according to theIEEE802. 11 system.

[0047]FIG. 17 shows an example of the frame structure according to theHiperLAN system.

BEST MODE OF CARRYING OUT THE INVENTION

[0048] The invention will be hereafter described in detail by referringto the attached drawings.

First Embodiment

[0049]FIG. 1 shows a block diagram of a base station and a mobilestation in a wireless communication system according to the firstembodiment of the invention.

[0050] Referring to FIG. 1, numeral 30 designates a base station in thewireless communication system, and numeral 40 designates a mobilestation that communicates wirelessly with the base station 30. The basestation 30 includes a central control unit 31.

[0051] The base station 30 comprises a central control unit 31 forallocating bands in a frame of a communication frequency in response toa band allocation request; an antenna 32 for wireless transmission andreception; a wireless processing means 33 for detecting availablefrequencies; a frame processing means 34 for carrying out frameprocessing by which control information such as allocated bandallocation information is converted into transmission data; a wirelesscontrol means 35 for creating control information such as a framesynchronizing signal and band allocation information concerningallocations by the central control unit 31; and a line processing means36 for sending external transmission data to the frame processing means34 in a certain format in response to an instruction from the wirelesscontrol means 35. The central control unit 31 carries out calculationsfor time allocation, for example, and it may be either included in thebase station 30, as according to the present embodiment, or locatedoutside the base station 30.

[0052] The mobile station 40 comprises an antenna 42 for wirelesstransmission and reception; a wireless processing means 43 for receivingcommunication data and sending it to the frame processing means 44; aframe processing means 44 for achieving frame synchronization based on acontrol signal received from the base station 30 and separating thecommunication data into control information and reception data; awireless control means 45 for decoding the band allocation informationand the like and preserving it as control information for use in thecommunication data transmission/reception processing; and a lineprocessing means 46 for sending external transmission data to the frameprocessing means 44 in a certain format in accordance with aninstruction from the wireless control means 45.

[0053] The wireless control processing means 45 notifies the wirelessprocessing means 43 of the start of a transmission/reception operationupon encountering an allocated band (time) in a frame. In the case ofinter-mobile station direct communication, the wireless controlprocessing means 45 notifies the wireless processing means 43 of achange of frequency to that used for inter-mobile station directcommunication.

[0054] In accordance with the present embodiment, the wirelesscommunication system comprises a synchronizing means for synchronizing,when a second frequency is to be used for inter-mobile station directcommunication that is different from a first frequency used for basestation-mobile station communication, frames between the basestation-mobile station communication and the inter-mobile station directcommunication, on the basis of control information used in the basestation-mobile station communication. The wireless communication systemalso comprises an allocation means for allocating bands and a frequencyfor inter-mobile station direct communication in accordance with anallocation request from the base station 30 or mobile station 40. Thebase station 30 and mobile station 40 each comprise a transmission meansand a reception means for transmitting and receiving allocation requestsand allocation notifying information between them. The mobile station 40further comprises a control means for changing the wireless frequency inaccordance with an allocation. Thus, a base station-mobile stationcommunication can be carried out simultaneously with an inter-mobilestation direct communication. The base station 30 also carries outcarrier sensing at a plurality of available frequencies and comprises ameans for carrying available frequencies other than that used by thebase station 30.

[0055]FIG. 2 shows an example of frame structure in inter-mobile stationdirect communication according to the present wireless communicationsystem, showing examples of frame structure and band allocation. Theframe structures correspond to those of the conventional example shownin FIG. 15.

[0056] Referring to FIGS. 2(a) and (b), the frame structure is dividedinto time regions consisting of control information 50, a communicationband DOWN-LINK 51, and a communication band UP-LINK 52. The controlinformation 50 includes information for a plurality of mobile stations40 to achieve synchronization with a base station 30 in each frame (atpredetermined periods), and information indicating a band (time region)in a frame allocated to each mobile station. The DOWN-LINK 51 is forsending data from the base station 30 to the mobile stations 40. TheUP-LINK 52 is for sending data from the mobile stations 40 to the basestation 30. The control information 50 includes a preamble 200 forbroadcast and a data payload 201, as described with reference to FIG.13(c). The preamble 200 for broadcast includes a synchronizing signalfor the mobile stations in a wireless cell to achieve synchronizationwith the base station, and control information such as frame structureinformation and band allocation information.

[0057] Referring to FIG. 2(b), a mobile station carries out inter-mobilestation direct communication at an inter-mobile station directcommunication frequency which is different from the frequency at whichframe synchronization is achieved and communication is carried out basedon the control information 50 transmitted by the base station 30. Themobile station synchronizes frames between base station-mobile stationcommunication and inter-mobile station direct communication by utilizingthe base station-mobile station communication control information 50instead of the control information 53 for the conventional inter-mobilestation direct communication. Numeral 54 designates a directcommunication band.

[0058]FIG. 2(c) shows an example of band allocation in basestation-mobile station communication. Numeral 55 designates controlinformation where the control information 50 is allocated. Numeral 56designates a band D1 where the DOWN-LINK 51 is allocated. Numeral 57designates a band U1 where the UP-LINK 52 is allocated.

[0059]FIG. 2(d) shows an example of band allocation in inter-mobilestation direct communication. As described above, the controlinformation (control information 53) for the conventional inter-mobilestation direct communication is not used, because the basestation-mobile station communication control information 50 is also usedfor the inter-mobile station direct communication. Numeral 58 designatesa band Di1 where the direct communication band 54 is allocated.

[0060] Thus, by synchronizing frames between base station-mobile stationcommunication and inter-mobile station direct communication, it becomespossible to process in parallel the communication band DOWN-LINK51 fromthe base station 30 to the mobile stations 40, the communication bandUP-LINK52 from the mobile stations 40 to the base station 30, and thedirect communication band 54 from one mobile station 40 to anothermobile station 40.

[0061] Hereafter, the operation of the wireless communication system asconfigured above will be described.

[0062]FIG. 3 shows a block diagram of an example of a wireless LAN basedon the present wireless communication system. Parts or elements similarto those shown in FIG. 14 are designated by similar references.

[0063] In FIG. 3, a wireless LAN 8 is comprised of a plurality of mobilestations 40A to 40C, and a base station 30 with a central control unit31 built inside. The wireless LAN 8 is connected to a WAN 7 via the basestation 40.

[0064] The mobile stations 40A to 40C are similar in structure to thosemobile stations 40 shown in FIG. 1, and they carry out basestation-mobile station communication in accordance with band allocationinformation notified from the base station 40. The communication pathsare indicated by communication paths 14 to 16. A communication path forinter-mobile station direct communication between the mobile station 40A(mobile station <1>) and the mobile station 40B (mobile station <2>) isindicated by a communication path 17.

[0065] An example of band allocation for the base station 30 and themobile station 40A (mobile station <1>) that wants to communicate withthe mobile station 40B (mobile station <2>) will be described byreferring to FIG. 2.

[0066] In FIGS. 2 and 3, the mobile station 40A (mobile station <1>)receives frame synchronization and band allocation based on the controlinformation 55 from the base station 30. A band 56 (band D1) is acommunication band from the base station 30 to the mobile station 40A(mobile station <1>). A band 57 (band U1) is a communication band fromthe mobile station 40A (mobile station <1>) to the base station 30. Aband 58 (band Di1) is a communication band from the mobile station 40A(mobile station <1>) to the mobile station 40B (mobile station <2>). Bycarrying out communication according to these allocations, the mobilestation 40A (mobile station <1)) can perform data communicationsimultaneously with the mobile station 40B (mobile station <2>) and thebase station 30 without interrupting its connection with the basestation 30.

[0067]FIG. 4 shows a control sequence chart indicating the flow of datain the above example of communication. The numbers in the drawing showthe individual processing steps.

[0068] In FIG. 4, it is assumed that the mobile station 40A (mobilestation <1>) and the mobile station 40B (mobile station <2>) havecompleted connection with the base station 30 and have startedcommunication therewith (60).

[0069] Initially, the mobile station 40A (mobile station <1>) transmitsa request (61) and another request (62) to the base station 30 in anallocated band of the UP-LINK 52. The request (61) calls for theallocation of a band for inter-mobile station direct communication fortransmitting data to the mobile station 40B (mobile station <2>). Therequest (62) calls for the allocation of a band for normal basestation-mobile station communication.

[0070] The mobile station 40B (mobile station <2>) also transmits arequest (63) to the base station 30 in an allocated band of the UP-LINK52, calling for the allocation of a band for normal base station-mobilestation communication.

[0071] The base station 30 then transmits an allocation request (64) tothe central control unit 31 which bundles the band allocation requestinformation from each mobile station and the band allocation requestfrom the base station 30 to the mobile station.

[0072] The central control unit 31, in response to the band allocationrequest (64), notifies the base station 30 of information about theallocations of bands in the next frame of the base station-mobilestation communication frequency and the inter-mobile station directcommunication frequency (65).

[0073] The base station 30 transmits, in the control information band inthe next frame, information about the band and frequency allocation fordirect communication from the mobile station 40A (mobile station <1>) tothe mobile station 40B (mobile station <2>) (66), and basestation-mobile station communication band allocation information (67,68) to the mobile station 40A (mobile station <1>) and the mobilestation 40B (mobile station <2)). Each mobile station carries outreception processing on the control information band.

[0074] The base station 30, in an allocated band in the DOWN-LINK 51 atthe base station-mobile station communication frequency, transmits basestation-mobile station communication data (69, 70) to the mobile station40A (mobile station <1>) and the mobile station 40B (mobile station<2>). Each mobile station carries out reception processing on anallocated band.

[0075] The mobile station 40A (mobile station <1>) transmitsinter-mobile station direct communication data (71) to the mobilestation 40B (mobile station <2>) in an allocated band for directcommunication of the inter-mobile station direct communicationfrequency. The mobile station 40B (mobile station <2>) carries out areception processing on an allocated band.

[0076] The mobile station 40A (mobile station <1>) and the mobilestation 40B (mobile station <2>) transmit base station-mobile stationcommunication data (72, 73) to the base station 30 on an allocated bandin the UP-LINK 52. The base station 30 carries out a receptionprocessing on an allocated band.

[0077]FIG. 5 shows a flowchart of the communication processing in thebase station 30. S indicates the steps thereof.

[0078] Initially, in a carrier sensing process in step S11, availablefrequencies are detected by the wireless processing means 33 (FIG. 1) ofthe base station 30. Of the frequencies that are detected, one that isused by the base station 30 is selected, and preparations are made fortransmission and reception. At the same time, notification offrequencies available for inter-mobile station direct communication isgiven to the central control unit 31. Simultaneously, notification ofavailable frequencies other than those used by the base station 30 isgiven to the central control unit 31.

[0079] In the process of transmitting a control signal in step S12, thewireless control means 35 creates control information including a signalfor frame synchronization and band allocation information allocated bythe central control unit 31. The control information is converted intotransmission data by the frame processing means 34, and then transmittedvia the wireless processing means 33 and antenna 32.

[0080] In the process of transmitting the communication data in stepS13, the line processing means 36 transmits external transmission datato the frame processing means 34 in accordance with instructions fromthe wireless control means 35. The data is converted into transmissiondata by the frame processing means 34 and then transmitted via thewireless processing means 33 and antenna 32.

[0081] In the process of receiving the communication data in step S14,the wireless signal is received by the antenna 32 and the wirelessprocessing means 33. The received data is separated into controlinformation and reception data by the frame processing means 34. Thecontrol information such as a band allocation request is processed bythe wireless control means 35, and necessary information is transmittedto the central control unit 31, where it is processed. The receptiondata is transmitted to the outside by the line processing means 36 afterbeing set in an external format.

[0082] In step S15, it is determined whether or not communication isfinished. If not, the process resumes from step S11 and theabove-described steps are repeated. If the communication is finished,the present process comes to an end.

[0083]FIG. 6 shows a flowchart of the communication processing performedin the mobile station.

[0084] In a carrier sensing step of step S21, available frequencies aredetected by the wireless processing means 43.

[0085] In the process of receiving the control signal in step S22, framesynchronization is carried out based on the control signal transmittedfrom the base station 30 and received by the antenna 42 and the wirelessprocessing means 43. The control signal is converted into controlinformation by the frame processing means 44. The wireless controlprocessing means 45 decodes band allocation information and the likefrom the control information and stores it as control information foruse during the process of transmitting and receiving communication data.

[0086] Upon reaching an allocated band (time) in a frame, the wirelesscontrol processing means 45 notifies the wireless processing means 43 ofthe start of a transmission/reception operation. In step S23, it isdetermined whether or not the communication is inter-mobile stationdirect communication. If so, the wireless processing means 43 isnotified of a change of frequency to that used for inter-mobile stationdirect communication in step S24. The transmission/reception frequencyis then changed and the routine progresses to step S25. If thecommunication is not inter-mobile station direct communication, theroutine progresses to step S25.

[0087] In the process of transmitting and receiving communication datain step S25, the wireless processing means 43 receives the communicationdata and sends it to the frame processing means 34, where the data isseparated into control information and reception data. The controlinformation is processed by the wireless control means 35. The receptiondata is sent to the outside by the line processing means 36 after beingset in an external format. External transmission data is sent by theline processing means 36 to the frame processing means 34 in accordancewith an instruction from the wireless control means 35, where the datais converted into transmission data and then transmitted by the wirelessprocessing means 43 and antenna 42.

[0088] In step S26, it is determined whether or not there is a band. Ifthere is a band, the routine returns to step S23 to repeat theabove-described processes. If not, it is determined in step S27 whetheror not communication is finished. If not, the routine returns to stepS21 to repeat the relevant steps. If the communication is finished, thepresent process comes to an end.

[0089] Thus, in accordance with the present embodiment, the wirelesscommunication system comprises a synchronization means for, when thecentral control unit 31 uses a second frequency for inter-mobile stationdirect communication which is different from the first frequency usedfor base station-mobile that communication, synchronizing frames betweenbase station-mobile station communication and inter-mobile stationdirect communication based on the control information used in basestation-mobile station communication. The system also comprises anallocation means for allocating a band and frequency for theinter-mobile station direct communication in accordance with anallocation request from the base station 30 or the mobile stations 40.Because the control information 55 for base station-mobile stationcommunication is utilized instead of the control information for thenormal inter-mobile station direct communication in synchronizing framesbetween base station-mobile station communication and inter-mobilestation direct communication, it is possible to process in parallel theband DOWN-LINK 51 for communication from the base station 30 to themobile stations 40, the band UP-LINK 52 for communication from themobile stations 40 to the base station 30, and the band 54 forcommunication from one mobile station 40 to another mobile station 40.

[0090] Thus, an inter-mobile station direct communication and a basestation-mobile station communication can be simultaneously conducted, orthe inter-mobile station direct communication can be conducted whilemaintaining connection with the base station 30, even when theinter-mobile station direct communication is conducted at a frequencyother than that of the base station 30.

[0091] Further, because the base station controls the inter-mobilestation direct communication, the burden on the mobile stations can bereduced.

Second Embodiment

[0092] In the second embodiment, the manner in which communication bandsare allocated is changed.

[0093]FIG. 7 shows a control sequence illustrating the flow of data inthe wireless communication system according to the second embodiment ofthe invention. FIG. 8 shows a block diagram of band allocation in thepresent wireless communication system, which corresponds to FIG. 2.

[0094] A wireless LAN can be constructed by using the present wirelesscommunication system in the same manner as described in FIG. 3.

[0095] Referring to FIG. 7, it is assumed that the base station 30,mobile station 40A (mobile station <1>), mobile station 40B (mobilestation <2>), and mobile station 40C (mobile station <3>) all have theircommunication lines open (80).

[0096] The mobile station 40C (mobile station <3>) transmits acommunication band request (81) to the base station. The mobile station40A (mobile station <1>) transmits a communication band request (82) tothe mobile station 40B (mobile station <2>).

[0097] In response to these band requests, the central control unit 31allocates a band 92 (band D1) and a band 93 (band U1) as communicationbands between the base station 30 and the mobile station 40C (mobilestation <3>) (83). The central control unit 31 also allocates a band 94(band D2) and a band 95 (band U2) as communication bands between themobile station 40A (mobile station <1>) and the mobile station 40B(mobile station <2>) (84). Numeral 91 designates control information.According to these allocations, the base station 30 and the mobilestation 40C (mobile station <3>) communicate with each other (85, 87),while the mobile station 40A (mobile station <1>) and the mobile station40B (mobile station <2>) communicate with each other (86, 88).

[0098] In accordance with the wireless communication system of thepresent embodiment, the base station 30 instructs that the inter-mobilestation direct communication between the mobile station 40A (mobilestation <1>) and the mobile station 40B (mobile station <2>) beconducted at a frequency other than that of the base station 30. Thus,the base station 30 can communicate with the mobile station 40C (mobilestation <3>).

[0099] When the direct communication between the mobile station 40A(mobile station <1>) and the mobile station 40B (mobile station <2>) isconducted at the same frequency as that of the base station 30, the basestation30 cannot transmit or receive data on that band. However, inaccordance with the present embodiment, the base station 30 can transmitand receive data on all of the bands (times) in the frame because thedirect communication between the mobile stations 40A and 40B isconducted at a different frequency.

[0100] Thus, an efficient wireless communication system can be realizedin which a single base station can use a plurality of frequencies forcommunication.

Third Embodiment

[0101] This is an example where the manner in which communication framebands are allocated is changed.

[0102]FIG. 9 shows a block diagram of frame allocation in the wirelesscommunication system according to the third embodiment of the invention,indicating examples of band allocations in frames for the basestation-mobile station communication frequency and the inter-mobilestation direct communication frequency.

[0103] A wireless LAN can be constructed using the present wirelesscommunication system in the same manner as described in FIG. 3.

[0104] Referring to FIGS. 3 and 9, the base station 30 broadcasts framesynchronization and band allocations in control information 100.Down-link phases D1 (101), D2 (102), D3 (104), and D4 (103) areallocated bands for transmission from the base station 30 to the mobilestation 40A (mobile station <1>), mobile station 40B (mobile station<2>), mobile station 40C (mobile station <3>), and mobile station 40D(mobile station <4>) (not shown in FIG. 3), respectively. Similarly,Up-link phases U1 (107), U2 (108), U3 (106), and U4 (105) are allocatedbands for transmission from the mobile station 40A (mobile station <1>),mobile station 40B (mobile station <2>), mobile station 40C (mobilestation <3>), and mobile station 40D (mobile station <4>), respectively,to the base station 30. Al (109) is an allocation band for a directcommunication between the mobile station 40A (mobile station <1>) andthe mobile station 40B (mobile station <2>). While in this example thenumber of the direct communication frequency is one, there may be morethan one such frequency as long as they can be used in the wirelesscommunication system.

[0105]FIG. 10 shows an example of communication between the base stationand the mobile stations in the present wireless communication system,illustrating the state of communication at each communication terminalallocated in FIG. 9.

[0106] The base station 30 broadcasts the control information (includingband allocation information) for frame synchronization, transmitsinformation to the individual mobile stations in D1, D2, D3, and D4, andreceives information from the individual mobile stations in U1, U2, U3,and U4. In this example, the states of communication in about fourframes are illustrated on the assumption that there is no change inallocations.

[0107] The mobile station 40A (mobile station <1>) receives the controlinformation from the base station 30, receives information from the basestation 30 in D1, and transmits information to the base station 30 inU1. The mobile station 40A (mobile station <1>) carries out a directcommunication with the mobile station 40B (mobile station <2>) in anallocation Al at a frequency different from that for the basestation-mobile station communication, as shown in the second and thirdframes from the head.

[0108] Thus, the mobile station 40A (mobile station <1>) can directlycommunicate with the mobile station 40B (mobile station <2>) while atthe same time communicating with the base station 30. Further, becausethe direct communication is carried out at a separate frequency, thebase station 30 can communicate with the mobile station 40C (mobilestation <3>) and mobile station 40D (mobile station <4>), even while thedirect communication is taking place.

Fourth Embodiment

[0109] This is an example where the manner in which bands in acommunication frame are allocated is changed.

[0110]FIG. 11 shows a block diagram of frame allocation in the wirelesscommunication system according to the fourth embodiment of theinvention, illustrating examples of band allocations in frames for basestation-mobile station communication and inter-mobile station directcommunication frequencies.

[0111] A wireless LAN can be constructed by using the present wirelesscommunication system in the same manner as described in FIG. 3.

[0112] Referring to FIGS. 3 and 11, for the base station-mobile stationcommunication frequency, control information (110) for framesynchronization, Down-link phases D1 (111), D2 (112), D3 (114), and D4(113) are allocated bands for transmission from the base station to themobile station 40A (mobile station <1>), mobile station 40B (mobilestation <2>), mobile station 40C (mobile station <3>), and mobilestation 40D (mobile station <4>) (not shown in FIG. 3), respectively.Up-link phases U1 (117), U2 (118), U3 (116), and U4 (115) are allocatedbands for transmission from the mobile station 40A (mobile station <1>),mobile station 40B (mobile station <2>), mobile station 40C (mobilestation <3>), and mobile station 40D (mobile station <4>), respectively,to the base station. A1 (121), A2 (120), A3 (123), A4 (119), and A5(122) are allocations for direct communication between the mobilestations <2>and <3>, the mobile stations <1>and <3>, the mobile stations<1>and <2>, the mobile stations <1>and <4>, and the mobile stations<3>and <4>.

[0113]FIG. 12 shows an example of communication between the base stationand the mobile stations in the present wireless communication system,illustrating the state of communication at each communication terminalallocated in FIG. 11.

[0114] For example, in D1 where the mobile station 40A (mobile station<1>) is communicating with the base station, the mobile station 40A(mobile station <1>) cannot communicate with any other mobile stationunless the mobile station 40A (mobile station <1>) is provided with aplurality of wireless transmission/reception units.

[0115] Thus, the central control unit 31 (FIG. 3) provides allocationsfor direct communication in bands other than D1, as shown in FIG. 12.

[0116] In the present embodiment, the central control unit 31 calculatescombinations for carrying out base station-mobile station communicationand inter-mobile station direct communication based on the bandallocation requests from each mobile station and the base station,provides efficient allocations that maximally utilize the wirelessbands, as shown in FIG. 11, and notifies the base station 30 as well asbroadcasts to each mobile station about their allocations. By such acentralized manner of control, frequencies can be completely utilizedwithout the stand-by times for avoiding collision of signals that arerequired in autonomous decentralized systems such as according toIEEE802, 11. Furthermore, the central management of the requests forinter-mobile station direct communication and base station-mobilestation communication by the single central control unit 31 allowstransmission and reception to occur without collision of allocations.

[0117] In the above-described embodiments, the invention is applied to awireless communication system comprising the base station 30, the mobilestations 40 wirelessly connected to the base station 30, and the centralcontrol unit 31 provided within the base station 30 for allocating bandsin the frames of communication frequencies in response to bandallocation requests. However, the invention can be applied to any systemas long as it is a TDMA-based wireless communication system. Forexample, the invention can be applied to cordless telephone systems inwhich a master unit is connected to a plurality of slave units viawireless communication, PDAs (Personal Digital Assistants) with wirelesscommunication capabilities, and small-sized notebook personal computers.

[0118] The wireless communication system may also be comprised of aplurality of identical wireless terminals having functions both as basestations, namely masters that manage communications, and as mobilestations, namely slaves that follow the master's instructions, eachwireless terminal carrying out both base station and mobile stationoperations.

INDUSTRIAL FIELD OF APPLICABILITY

[0119] Thus, the wireless communication system according to theinvention allows inter-mobile station direct communication and basestation-mobile station communication to take place simultaneously, orinter-mobile station direct communication to take place whilemaintaining connection with the base station, when inter-mobile stationdirect communication is carried out at a frequency other than that ofthe base station.

[0120] Further, because the base station controls inter-mobile stationdirect communication, the burden on the mobile stations can be reduced.

[0121] Further, because inter-mobile station direct communication can becarried out at a second frequency that is different from the firstfrequency used in base station-mobile station communication, the basestation can carry out transmission or reception of data even in timeregions where inter-mobile station direct communication is taking place,for example. Thus, an efficient wireless communication system can berealized in which the base station can utilize a plurality offrequencies for communication.

1. A wireless communication system comprised of a base station and mobile stations wirelessly connected to the base station, wherein the mobile stations can communicate with one another without the intervention of the base station, the system further comprising a synchronizing means, wherein when a second frequency is used for inter-mobile station direct communication that is different from a first frequency used for a base station-mobile station communication, the synchronizing means synchronizes a frame in base station-mobile station communication with that in inter-mobile station direct communication based on control information used in base station-mobile station communication.
 2. A mobile station wirelessly connected to a base station and capable of base station-mobile station communication at a first frequency and inter-mobile station direct communication at a second frequency that is different from the first frequency without the intervention of the base station, the mobile station comprising a synchronizing means for synchronizing a frame in base station-mobile station communication with that in inter-mobile station direct communication based on control information used in base station-mobile station communication.
 3. A base station in a wireless communication system comprised of the base station and mobile stations wirelessly connected to the base station, the base station comprising an allocation means for allocating a second frequency for inter-mobile station direct communication, which is different from a first frequency used for base station-mobile station communication in response to a request from a mobile station.
 4. A base station in a wireless communication system comprised of the base station and mobile stations wirelessly connected to the base station, the system capable of conducting base station-mobile station communication at a first frequency and inter-mobile station direct communication at a second frequency different from the first frequency without the intervention of the base station, the base station comprising: an allocation means for allocating bands in a frame for inter-mobile station direct communication based on a request from a mobile station.
 5. The base station according to claim 3, further comprising a carrying means for performing carrier sensing at a plurality of available frequencies and carrying available frequencies other than the frequency used by the base station. 